Off‐Stoichiometry Synthesis of 0D Metal Halide Polycrystals for High‐Performance X‐Ray Imaging

Abstract 0D organic–inorganic metal halides (OIMHs) with intriguing luminescence encoded in their diverse crystal structure open wide opportunities for next‐generation optoelectronics. Yet, this structural diversity makes their precise synthesis challenging. Here, a facile yet efficient off‐stoichiometry antisolvent precipitation protocol is devised to synthesize pure Bmpip2PbBr4 (Bmpip = 1‐butyl‐1‐methylpiperidinium) polycrystals. Optical investigations reveal that the key to suppressing the by‐product, Bmpip9[Pb3Br11][PbBr4]2, generally occurring in a typical stoichiometric synthesis is to create a Br‐rich environment to promote the [PbBr4]2− formation while suppressing the formation of [Pb3Br11]5−. Moreover, this off‐sociometric protocol can be extended to the precise synthesis of Bzmim3SbCl6 (Bzmim = 1‐benzyl‐3‐methylimidazolium) polycrystals through the meticulous control of [SbCl6]3− formation in the solution. The resulting Bzmim3SbCl6 polycrystals show a nominal light yield of 24600 photons MeV−1, which is 6.8 times higher than that of its by‐product, namely Bzmim2SbCl5, and outperforms that of commercial LuAG:Ce. As a result, the scintillators made of Bzmim3SbCl6@PMMA achieve a decent spatial resolution of 8.3 lp mm−1. This work highlights the importance of regulating the metal polyhalide intermediates in precisely synthesizing 0D OIMHs.